The Application and Development of Wood Plastics

Wood-plastic composites (Wood-Plastic Composites, WPC) is a new type of composite material that has flourished at home and abroad in recent years. It refers to the use of polyethylene, polypropylene and polyvinyl chloride instead of the usual resin adhesives. More than 35%-70% of wood flour, rice husk, straw and other waste plant fibers are mixed into new wood materials, which are then subjected to plastic processing techniques such as extrusion, molding, and injection molding to produce plates or profiles. Mainly used in building materials, furniture, logistics packaging and other industries. A board that is formed by hot extrusion after mixing plastic and wood powder in a certain proportion is called an extruded wood-plastic composite board.

Application of WPC Products:

Wood plastic interior doors, skirting lines, overall cabinets, wardrobes, exterior wall hanging panels, ceilings, decorative wall panels, outdoor floors, guardrail columns, plastic steel pavilions, garden guardrails, balcony guardrails, garden fences, leisure benches, trees Pools, flower racks, flower box air conditioner racks, air conditioner shields, blinds, road signs, transportation pallets, etc.

The application of wood plastic materials is flexible and can be applied to any field of wood processing. It is the best environmentally friendly material to replace wood; wood plastic products play a vital role in the country’s low energy consumption and are a recyclable product. It is widely used in several major projects.

The Category of Plastic Wood:

After the concept and products of wood plastic were brought into the domestic market, they were favored by some companies and consumers, and then wood plastic products appeared in the building materials market. The main domestic wood plastic materials are divided into two categories: PE wood plastic and PVC wood plastic.

PE Wood

The advantages of PE wood plastic:

PE wood-plastic material has excellent waterproof and anti-corrosion properties, high hardness, and can be deformed and buckled when heated, but it has a good effect with thickened or porous hollow structure.

Disadvantages of PE wood plastic:

1. The product can be used outdoors for a limited number of years; current use is 3-5 years;

2. The anti-oxidation and anti-photolysis ability is poor, even if the anti-oxygen agent and UV reference agent are added, the effect is not ideal, and it will also affect the product strength and color fastness;

3. The appearance of the product is pure in color, without woodiness, and the appearance effect is poor.

PVC Wood

The advantages of PVC wood plastic:

1. PVC wood-plastic products can be made of new materials or old materials (while PE made of new materials will cost too much and the product cannot enter the market), modification is also relatively easy, and the amount of supplement depends on the quality of production Depending on

2. PVC can be made into low-foaming wood-plastic products, so the cost is lower, and the co-extrusion form (two-material multi-material co-extrusion or steel-plastic co-extrusion) can be used if it is deemed appropriate, and the strength and wood grain feel are good;

3. PVC can be processed twice. Variety of surface decorations or paint covering UV paint, the product looks good and the color fastness is good;

4. The waterproof and anticorrosive properties of PVC wood plastic products are also excellent.

The difference between PE wood plastic and PVC wood plastic

① Different manufacturing methods: the preparation of PE wood-plastic products mainly adopts the cold push method; the preparation of PVC wood-plastic products can be divided into vacuum forming, cold push and three-roll restraint.

②Different raw materials: PE wood-plastic materials are mainly secondary and tertiary PE recycled materials plus wood powder, calcium powder and a small amount of modifiers. The materials used to manufacture PVC wood plastic are mainly PVC resin powder, PVC recycled materials, wood powder, stone powder and some modifiers, etc.

③Different performance: PE wood plastic products are heavy, with high hardness, high brittleness, and high creep. PVC wood plastic products have light weight, poor hardness, good toughness, and creep, and are not as large as PE wood plastic products.

④Different uses: PE wood plastic products are mainly based on outdoor garden construction, green wood such as guardrails, floors, trash cans, flower ponds, pallets and so on. PVC wood plastic products are mainly indoor decorative materials, such as doors, floors, skirting, door covers and so on.

ABS Wood:

There is also a better classification of wood plastic materials-ABS wood plastic. ABS wood plastic products are easy to process and have good strength. They can also be used for wood grain effects, so they are not easy to damage.

Processing of Wood Plastics:

Some artificial zeolite can be added to the polymer. This aluminosilicate molecule captures the powder and can absorb the peculiar smell in the material. Through a large number of crystalline cavities in the powder, the adsorbent can capture small organic molecules that produce peculiar smell. Molecular capture adsorbents have been successfully applied to polyolefin extrusion pipes, injection and extrusion blow molding utensils, insulation packaging materials, extrusion outer packaging and sealing materials. Molecular adsorption powder can also be used as a desiccant to be added to plastics to remove moisture.

Extruded products of different sizes and shapes increase the diversity of wood-plastic composites.

When the profile is not required to have a continuous sheet structure or the components have a complicated structural design, the wood-plastic profile can be formed by injection molding or compression molding. Processors sometimes have to face the problem of how to completely fill the wood-plastic material during processing. In order to solve this problem, they need to reduce the amount of wood filler to increase the fluidity of the melt.

Since 200°C is the upper limit of the processing temperature for wood-plastic composites, some resins with melting points above 200C, such as PET, cannot be used for wood-plastic composites.

Moisture will degrade the performance of the composite material and also help to breed microorganisms, so the moisture must be removed before using the wood filler. The wood filler should be dried before processing, and the moisture content after treatment is generally required to be less than 1~2%.

Wood-plastic composite material processing machinery is required to be equipped with feeding equipment, drying equipment, extrusion equipment and molding equipment, as well as some necessary downstream equipment such as cooling water tanks, traction equipment and cutting equipment.

Wood Plastic Treatment:

Appropriate additives are needed to modify the surface of polymer and wood flour to improve the interface affinity between wood flour and resin.

High-filled wood powder has a poor dispersion effect in molten thermoplastics, resulting in poor melt fluidity and difficulty in extrusion molding. Surface treatment agents can be added to improve fluidity to facilitate extrusion molding.

The plastic matrix also needs to add various additives to improve its processing performance and the use performance of its products.

Feeding process:

The wood flour has a fluffy structure, and it is not easy to feed the extruder screw, especially when the wood flour contains more water, the phenomenon of "bridging" and "holding the pole" often occurs.

The instability of feeding will cause extrusion fluctuations, resulting in a decrease in extrusion quality and output. Feeding is interrupted, and the residence time of the material in the barrel is prolonged, causing the material to burn and change color, which affects the internal quality and appearance of the product.

Use forced feeding device and reasonable conveying method to ensure the stability of extrusion.

Exhaust during processing:

The small molecular volatile substances and moisture contained in wood flour can easily bring defects to the product, and the pre-treatment cannot completely remove them. Therefore, the design of the exhaust system of the wood-plastic composite extruder should be paid more attention than the ordinary plastic extruder, and multi-stage exhaust can be carried out if necessary.

To a large extent, the better the exhaust effect, the better the quality of extruded products.